Indiana University Bloomington

Star Trak: August 2014

  • July 30, 2014

FOR IMMEDIATE RELEASE

BLOOMINGTON, Ind. -- The annual Perseid meteor shower, which will peak the night of Aug. 12-13, is one of the most popular every year because it happens on warm summer nights, perfect for gazing at the starry sky. In a clear dark sky there may be as many as 60 bright meteors per hour, some with smoke trails that last several seconds after the meteor has vanished.

This year the moon will be just two days past full at the shower’s peak, so many of the fainter meteors will be washed out by bright moonlight. Start observing around midnight local daylight time. If possible, position yourself so the moon is behind you and hidden behind a building or tree.

The Perseids will be visible for most of August, though there will be fewer meteors to see the further from the peak date you watch. If the peak is hidden by clouds, try looking for meteors again as soon as the night sky is clear. To minimize the effect of local light pollution, which can obscure as many as half of the meteors, try to avoid artificial lights. Face east if you have a clear view in that direction, and look about halfway up the sky from the horizon. You won't need binoculars or a telescope because the meteors move much too fast for those. The chances of seeing a fireball will be greatest near dawn, when Earth will be moving head-on into the meteor stream.

The Perseids may appear anywhere in the sky, but they will seem to originate from a point called the radiant in the constellation Perseus, which gives these “shooting stars” their name. The higher the radiant is above the northeastern horizon, the more meteors will be visible. Perseus is just north of the W-shaped constellation Cassiopeia in the Milky Way, with the bright star Capella and the Pleiades star cluster below it. Meteors near the radiant will have short trails because we see them nearly end on, while those far from the radiant will look longer because they are seen from the side.

Most meteor showers happen when Earth crosses the orbit of a comet; the Perseids come from Comet Swift Tuttle. The meteors are caused by particles released from the comet's nucleus and left behind in space. As Earth plows through this stream of debris, ranging in size from sand grains to pebbles, each particle slams into our atmosphere at a speed of more than 30 miles per second and burns up almost instantly from friction with air molecules. The resulting heat momentarily creates a streak of glowing air that we see as a meteor. All of this happens about 60 miles above the ground, regardless of how close some meteors may appear.

Planets

Venus and Jupiter, the two brightest planets, will have their closest conjunction since 2000 on the night of Aug. 17-18. Much brighter Venus will pass just 0.2 degrees north of Jupiter around midnight, and the pair will be about 5 degrees above the east-northeastern horizon an hour before sunrise. Telescopes and binoculars may show the Beehive star cluster (M44) less than 1 degree to their left (north).

As darkness falls during August, Saturn and Mars will come into view low in the southwest. Reddish Mars will begin the month to the right (west) of yellow Saturn, with the bright white star Spica about the same distance to the right of Mars. The two planets will move closer as the month goes by, and on Aug. 27 Mars will pass about 4 degrees south of Saturn. Saturn’s rings will be tilted 21 degrees to our line of sight.

Mercury will pass behind the sun Aug. 8 and then come into view very low in the west after sunset by month’s end. Observers at mid-northern latitudes will have difficulty spotting Mercury even with optical aid, but it will be much easier to see for those in the Southern Hemisphere.

Light pollution

If you look at the constellation Cassiopeia in the northeast on a clear summer night, and you can't see the Milky Way sprawling high across the sky from the northern to the southern horizon, then your sky has significant light pollution, which is the case for about two thirds of the world's population. This dimming of the night sky is caused by excessive artificial lighting, much of which is wasted. Visit the International Dark-Sky Association website for more information.

Moon phases

The moon will be at first quarter on Aug. 3, full on Aug. 10, at third quarter on Aug. 17 and new on Aug. 25.

Related Links

Perseid meteor shower

Photo by NASA

Print-Quality Photo

Media Contacts

Hal Kibbey

  • Office 812-336-1333
  • hkibbey@indiana.edu